In recent years, organic EL display panels that have a plurality of organic EL elements in rows above a substrate have been used as light-emitting display panels in compact electronic equipment and compact display devices. The basic structure of an organic EL element is to form a light-emitting layer, which includes organic light-emitting material, between a pair of electrodes, i.e. an anode and a cathode. When voltage is applied between the pair of electrodes, holes injected into the light-emitting layer from the anode recombine with electrons injected into the light-emitting layer from the cathode, and as a result, the organic EL element emits light. Since each organic EL element in the organic EL display panel emits light, the light from the display panel is highly visible.
In an organic EL display panel, typically a light-emitting layer is partitioned in each organic EL element by banks (walls) formed from insulating material. These banks define the shape of the light-emitting layer. Between the anode and the light-emitting layer, intermediate layers are provided as necessary, such as a hole-injection layer, hole transporting layer, or hole injection and transporting layer. An electron injection layer, electron transporting layer, or electron injection and transporting layer may also be provided between the cathode and the light-emitting layer as necessary.
In a full-color organic EL display panel, such organic EL elements are formed into sub-pixels whose color is R, G, or B. Three adjacent RGB sub-pixels together constitute one pixel.
In order to form the light-emitting layer or intermediate layers in each organic EL element, banks are formed on the substrate to partition adjacent organic EL elements. Subsequently, an inkjet or other wet method is generally used to spray ink containing high-polymer material or low-molecular material suitable for thin-film formation. With such a wet method, it is relatively easy to form the intermediate layer or light-emitting layer even in large panels.
In an inkjet method (see Patent Literature 1), which is representative of wet methods, inkjet heads are moved across a substrate, on which ink is to be sprayed, in any direction of the matrix of elements while a solution (hereinafter simply “ink”) is sprayed by ejecting drops of ink through each nozzle into regions defined by the banks on the substrate. The ink contains organic material and solvent that are for forming the intermediate layers, the light-emitting layer, etc.